JP2741702B2 - Evaporative fuel processor for internal combustion engines - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel vapor treatment system for an internal combustion engine, and more particularly to a fuel vapor treatment system capable of detecting the presence or absence of leakage in a fuel vapor emission suppression system.

[0002]

2. Description of the Related Art Conventionally, an evaporative fuel processing apparatus has been widely used in which evaporative fuel generated in a fuel tank is temporarily stored in a canister and the stored evaporative fuel can be appropriately purged into an intake system of an engine. Have been.

In this fuel vapor treatment apparatus, a fuel tank, a canister, and a passage connecting the fuel tank and the canister and a passage connecting the canister to an intake system of the engine are detected as abnormalities in the fuel vapor suppression system. The suppression system is set to a negative pressure state using the suction negative pressure of the engine, and then the presence or absence of leakage is detected based on a pressure change in the fuel vapor emission suppression system when the connection with the intake system of the engine is cut off. The applicant of the present application has already proposed the above (Japanese Patent Application No. 3-360630).

[0004]

However, in the above-mentioned conventional method, a pressure sensor is mounted on the fuel tank, and when the pressure in the tank decreases to a predetermined negative pressure P1 (see FIG. 2).
(D), at time t4), the connection to the intake system of the engine is cut off, and the presence / absence of leakage is detected based on the increase rate of the tank internal pressure from this point until a predetermined time has elapsed. There was a problem.

That is, when the tank internal pressure drops to the predetermined negative pressure P1, the canister internal pressure (see FIG. 2 (d)) is still lower, so that the tank internal pressure drops after time t4. It starts to rise from t5. Therefore, when the rate of increase of the tank internal pressure is calculated based on the tank internal pressure at time t4, the value becomes smaller than the originally required rate of increase (the rate of increase between times t5 and t6) (or the tank internal pressure at time t6 becomes lower than P1). ), Small leaks may not be detected.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has as its object to provide an evaporative fuel processing apparatus capable of more accurately detecting the presence or absence of a leak in an evaporative fuel emission suppression system. I do.

[0007]

To achieve the above object, the present invention provides a canister having a fuel tank, an intake port communicating with the atmosphere, and having activated carbon for adsorbing evaporated fuel generated in the fuel tank. A first passage connecting the canister to the fuel tank; a second passage connecting the canister to an intake system of an internal combustion engine; and a purge control valve interposed in the second passage. An evaporative fuel discharge suppression system, a drain shut valve for opening and closing the intake port of the canister, a pressure detecting means for detecting a pressure in the evaporative fuel discharge suppression system, and opening and closing the purge control valve and the drain shut Pressure-reducing processing means for introducing a negative pressure in the intake pipe of the engine by closing the valve to bring the evaporative fuel discharge suppression system into a predetermined negative pressure state and then closing the purge control valve; An evaporative fuel processing apparatus for an internal combustion engine, comprising: a leak detection unit configured to detect the presence or absence of a leak in the evaporative fuel discharge suppression system based on a decrease rate of the negative pressure after closing the purge control valve. When a predetermined delay time has elapsed from the end of the pressure reduction processing by the processing means, a delay means for operating the leak detection means is provided.

In addition, it is desirable that the pressure reduction processing means operates until the pressure detected by the pressure detection means drops by a predetermined pressure with respect to the pressure detected when the fuel vapor emission suppression system is open to the atmosphere. .

[0009] The leak detecting means may be configured to detect the pressure in the evaporative fuel discharge suppression system at the start of the operation and the pressure in the evaporative fuel discharge suppression system when a predetermined measurement time has elapsed from the start of the operation. It is desirable to detect the presence or absence of leakage of the fuel vapor emission suppression system based on this.

It is preferable that the predetermined delay time is a time until the pressures of the respective parts in the fuel vapor suppression system become substantially equal.

Preferably, the pressure detecting means is at least one of a tank internal pressure detecting means for detecting a pressure in the fuel tank and a canister internal pressure detecting means for detecting a pressure in the canister.

[0012]

The presence or absence of leakage of the evaporative fuel discharge suppression system is detected based on the rate of decrease of the negative pressure after a predetermined delay time has elapsed from the point in time when the decompression process for setting the evaporative fuel discharge suppression system to the predetermined negative pressure state is completed. You.

[0013] The evaporative fuel discharge suppression system is reduced in pressure until the pressure detected by the pressure detecting means drops by a predetermined pressure with respect to the detected pressure when the evaporative fuel discharge suppression system is open to the atmosphere.

[0014] The evaporative fuel discharge suppression system is based on the pressure in the evaporative fuel discharge suppression system when a predetermined delay time has elapsed from the end of the decompression process and the pressure in the evaporative fuel discharge suppression system when a predetermined measurement time has further elapsed. The presence or absence of leakage is detected.

[0015] The predetermined delay time is a time until the pressures of the respective parts in the evaporative emission control system become substantially equal.

[0016]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is an overall configuration diagram showing an embodiment of a fuel vapor processing apparatus for an internal combustion engine according to the present invention.

In FIG. 1, reference numeral 1 denotes an internal combustion engine having, for example, four cylinders (hereinafter simply referred to as "engine"). A throttle body 3 is provided in the middle of an intake pipe 2 of the engine 1. A throttle valve 3 'is provided. The throttle valve 3 'has a throttle valve opening (θ
A TH) sensor 4 is connected, and outputs an electric signal corresponding to the opening of the throttle valve 3 ′ and supplies it to an electronic control unit (hereinafter referred to as “ECU”) 5.

The fuel injection valve 6 is provided for each cylinder in the intake pipe 2 and slightly upstream of an intake valve (not shown) between the engine 1 and the throttle valve 3 '. Each fuel injection valve 6 is connected to a fuel pump 8 via a fuel supply pipe 7 and electrically connected to the ECU 5.
5 controls the valve opening timing of the fuel injection.

Downstream of the throttle valve 3 'of the intake pipe 2, a negative pressure communication path 9 and a purge pipe 10 are provided in a branched manner, respectively. The negative pressure communication path 9 and the purge pipe 10 are connected to a fuel vapor discharge suppression system 11 described later. It is connected to the.

Further, a branch pipe 12 is provided on the downstream side of the purge pipe 10 from the intake pipe 2, and an absolute pressure (PBA) sensor 13 is provided at a tip of the branch pipe 12. Also,
The PBA sensor 13 is electrically connected to the ECU 5,
Absolute pressure PB in intake pipe 2 detected by A sensor 13
A is converted into an electric signal and supplied to the ECU 5.

An intake air temperature (TA) sensor 14 is mounted on the intake pipe 2 downstream of the branch pipe 12.
4, the intake air temperature TA detected is converted into an electric signal,
It is supplied to the ECU 5.

An engine coolant temperature (TW) sensor 15 composed of a thermistor or the like is inserted into a cylinder wall of the cylinder block of the engine 1 filled with coolant, and the engine coolant temperature TW detected by the TW sensor 15 is converted into an electric signal. The converted data is supplied to the ECU 5.

An engine speed (NE) sensor 16 is provided around a cam shaft or a crank shaft (not shown) of the engine 1.
Is attached.

The NE sensor 16 outputs a signal pulse (hereinafter, referred to as a “TDC signal pulse”) at a predetermined crank angle position every time the crankshaft of the engine 1 rotates 180 degrees, and the TDC signal pulse is supplied to the ECU 5. .

The transmission 17 is interposed between wheels (not shown) and the engine 1, and the wheels are driven by the engine 1 via the transmission 17.

A vehicle speed (VSP) sensor 18 is attached to the wheels, and the vehicle speed VSP detected by the VSP sensor 18 is converted into an electric signal and supplied to the ECU 5.

In the middle of the exhaust pipe 19 of the engine 1, an oxygen concentration sensor (hereinafter referred to as "O ₂ sensor") 20 is provided.
The oxygen concentration in the exhaust gas detected by the O ₂ sensor 20 is converted into an electric signal,
Supplied to

An ignition switch (IGSW) sensor 21 is an IG indicating that the engine 1 is operating.
The ON state of the SW is detected and the electric signal is supplied to the ECU 5.

The fuel vapor emission control system 11 (hereinafter referred to as "emission control system") includes a fuel tank 23 having a filler cap 22 which is opened when fuel is supplied, and an activated carbon 24 as an adsorbent. A canister 26 provided with an intake port (outside air intake) 25 at the top,
A fuel vapor flow passage (first passage) 27 connecting the canister 26 and the fuel tank 23, a two-way valve 28 interposed in the fuel vapor flow passage 27, a canister 26 and the intake pipe 2 A purge passage (second passage) 10 to be connected;
A purge control valve 36 and a hot wire flow meter 37 provided in the middle of the purge passage 10 are provided.

The fuel tank 23 is connected to the fuel injection valve 6 via a fuel pump 8 and a fuel supply pipe 7, and has a tank internal pressure (PT) sensor 29 and a fuel amount (FV) sensor above it. A fuel temperature (TF) sensor 31 is provided on the side of the fuel cell 30.
Further, the PT sensor 29, the FV sensor 30, and the TF
Each of the sensors 31 is electrically connected to the ECU 5. Then, the PT sensor 29 detects the internal pressure (PT) of the fuel tank 23 and supplies the electric signal to the ECU 5,
The FV sensor 30 detects the amount of fuel (FV) in the fuel tank 23 and supplies an electric signal to the ECU 5 for further detecting the amount of fuel (FV).
The sensor 31 detects the fuel temperature (TF) in the fuel tank 23 and supplies an electric signal to the ECU 5.

The two-way valve 28 has a positive pressure valve 32 and a negative pressure valve 33, and the diaphragm 32 of the positive pressure valve 32
The rod 35a of the electromagnetic drive unit 35 is connected to a. The electromagnetic drive unit 35 is electrically connected to the ECU 5, and the operation state of the two-way valve 28 is controlled by a signal from the ECU 5. When the electromagnetic drive unit 35 is excited (turned on), the positive pressure valve 32 is forcibly pushed open, and the two-way valve 28 is opened. The directional valve 28 is
Only when the difference between the pressure on the canister 26 side and the pressure on the fuel tank 23 side is equal to or greater than a predetermined value, the valve is opened.

The purge pipe 10 connected to the canister 26
A purge control valve 36 is interposed in the pipeline, and a solenoid of the purge control valve 36 is connected to the ECU 5. Then, the purge control valve 36 is controlled in accordance with a signal from the ECU 5, and changes the valve opening amount linearly. That is, the ECU 5 outputs a desired control amount to control the opening amount of the purge control valve 36.

The canister 26 and the purge control valve 36
A hot-wire flow meter (mass flow meter) 37 is interposed between the two. The hot wire flow meter 37 utilizes the fact that the temperature decreases and the electrical resistance decreases when a heated platinum wire is exposed to an air current through an electric current, and its output characteristics include fuel vapor concentration, It changes according to the flow rate and the purge flow rate, and supplies an output signal corresponding to these changes to the ECU 5.

A drain shut valve 38 is connected to the intake port 25 of the canister 26 and communicates with the atmosphere.
Is interposed. The drain shut valve 38 is defined by a diaphragm 41 into an atmosphere chamber 42 and a negative pressure chamber 43. Further, the atmosphere chamber 42 connects the first chamber 44 having a valve body 44a therein, the second chamber 45 provided with an air inlet 45a, and the second chamber 45 and the first chamber 44. The valve body 44a is connected to the diaphragm 41 via a rod 48. In addition, the negative pressure chamber 43
Is provided with a spring 49 which communicates with the electromagnetic valve 39 and resiliently urges the diaphragm 41 in the direction of arrow A.

When the solenoid of the solenoid valve 39 is demagnetized (turned off), air is introduced into the negative pressure chamber 43 through the air supply port 50, and the drain shut valve 38 is opened.
When the solenoid of the solenoid valve 39 is excited (turned on), the solenoid valve 39 is connected to the intake pipe 2 through the negative pressure communication passage 9 and the drain shut valve 38 is closed. Incidentally, 51 is a check valve.

Thus, the ECU 5 has an input circuit having a function of shaping the input signal waveforms from the various sensors described above, correcting the voltage level to a predetermined level, converting an analog signal value to a digital signal value, and the like. A central processing circuit (hereinafter referred to as a “CPU”), storage means for storing an operation program executed by the CPU, an operation result, and the like; the fuel injection valve 6, the electromagnetic drive unit 35, the electromagnetic valve 39, and the purge control valve 36 And an output circuit for supplying a drive signal to the control circuit.

FIG. 2 is a diagram showing the operation pattern of the two-way valve 28, the drain shut valve 38, and the purge control valve 36 in this embodiment and the state of change of the tank internal pressure PT at that time. CPU).

First, during normal operation (normal purge mode) (shown in FIG. 2), the electromagnetic drive unit 35 is turned on, the two-way valve 28 is opened, and the drain shut valve 38 is opened. When the IGSW is turned on and the operation of the engine is detected by the IGSW sensor 18, the purge control valve 36 is opened. Then, the evaporated fuel generated in the fuel tank 23 flows into the canister 26 through the fuel vapor flow passage 27, and is temporarily absorbed and stored by the adsorbent 24 of the canister 26. Since the drain shut valve 38 is in the open state during the normal operation as described above, the outside air is supplied to the canister 26 from the air inlet 45a, and the fuel vapor flowing into the canister 26 is purged together with the outside air into the purge pipe 10 and the purge pipe 10. The air is purged to the intake pipe 2 via the control valve 36.

When the engine 1 satisfies a predetermined monitoring permission condition described later, the two-way valve 28, the drain shut valve 38, and the purge control valve 36 operate as follows, and the abnormality of the exhaust suppression system 11 Make a diagnosis.

First, the tank pressure PT is released to the atmosphere (shown in FIG. 2). That is, the two-way valve 28 is maintained in the open state to bring the fuel tank 23 into communication with the canister 26, the open state of the drain shut valve 38 is maintained, and the purge control valve 36 is further opened. The tank pressure PT is maintained and released to the atmosphere.

Next, the fluctuation amount of the tank internal pressure is measured (shown in FIG. 2).

That is, while the drain shut valve 38 is kept open and the purge control valve 36 is kept open, the two-way valve 28 is kept closed (the electromagnetic drive unit 3).
5 is turned off), the amount of change in the tank internal pressure from the time of opening to the atmosphere is measured, and the amount of generated steam in the fuel tank 23 is checked.

Next, the pressure of the emission suppression system 11 is reduced (FIG. 2,
). That is, the two-way valve 28 and the purge control valve 3
While maintaining the valve 6 in the open state, the drain shut valve 38 is closed, and the exhaust suppression system 11 is brought into a negative pressure state by the suction force from the intake pipe 2 generated through the purge pipe 10.

Next, a leak down check is performed (shown in FIG. 2).

That is, when the exhaust suppression system 11 is brought into a predetermined negative pressure state, the purge control valve 36 is closed, and the PT sensor 29
To check the change state of the tank internal pressure PT. If there is no leak from the discharge suppression system 11, the tank internal pressure PT
Changes as shown by the solid line, and it is determined that the emission suppression system 11 is normal. On the other hand, when the evaporated fuel is leaking from the emission suppression system 11, the tank internal pressure approaches the atmospheric pressure as shown by the dashed line. Therefore, the fuel vapor leaks from the emission suppression system 11, and it is determined that the emission suppression system 11 is abnormal. If the discharge suppression system 11 does not reach the predetermined negative pressure state within the predetermined time, the leak-down check is not performed as described later.

After the end of the abnormality determination, the routine shifts to the normal purge (shown in FIG. 2).

That is, while the two-way valve 28 is maintained in the open state, the drain shut valve 38 is opened and the purge control valve 36 is switched to the open state to perform normal purging.
At this time, the tank internal pressure PT is open to the atmosphere, and is substantially equal to the atmospheric pressure.

Hereinafter, a method of diagnosing abnormality of the emission suppression system 11 will be described in detail with reference to the flowcharts shown in the drawings.

FIG. 3 is a flowchart showing a control procedure of the abnormality diagnosis processing of the emission suppression system 11, and the control procedure is executed by the ECU 5 (CPU).

First, in step S1, a monitor permission determination routine, which will be described later, is executed. Next, in step S2, it is determined whether monitoring of abnormality diagnosis is permitted, that is, the flag FMO
It is determined whether N is set to “1”. If the answer is negative (NO), the two-way valve 28, the drain shut valve 38, and the purge control valve 36 are set to the normal purge mode (step S14), and the process ends, while the answer is affirmative (YES). In the case of ()), the tank pressure at the time of opening to the atmosphere is checked (step S3), and it is determined whether or not the check is completed (step S4). And
When the answer is negative (NO), the process is terminated as it is, while when the answer is affirmative (YES), that is, when it is determined that the check of the tank internal pressure is completed, the two-way valve 28 is closed next. Then, a change in the tank internal pressure is checked (step S5), and it is determined whether or not the check has been completed (step S6). When the answer is negative (NO), the process is terminated, while when the answer is affirmative (YES), the pressure reduction process of the emission suppression system 11 including the fuel tank 23 is performed (step S7).

On the other hand, at the same time as the start of the pressure reduction process, the ECU
Then, a first timer tmPRG built in 5 is started, and it is determined whether or not the timer value has exceeded a predetermined time T1 (step S8). Here, the predetermined time T1 is set to a time sufficient to bring the discharge suppression system 11 into a predetermined negative pressure state in a normal state. When the answer to step S8 is affirmative (YES), the emission suppression system 11 cannot be set to the predetermined negative pressure state because "perforation" or the like has occurred in the fuel tank 23 or the like. And the process proceeds to step S12. On the other hand, if the answer to step S8 is negative (NO), it is determined whether or not the decompression process has been completed (step S9). And the answer is negative (N
In the case of (O), the process is terminated, while the answer is affirmative (YE).
In the case of S), it is checked whether or not a fuel vapor leak has occurred from the emission suppression system 11 based on a leak down check routine to be described later (step S10), and then it is determined whether or not the check has been completed (step S10). Step S1
1).

If the answer is negative (NO), the process is terminated, while if the answer is affirmative (YES), the process proceeds to step S12.

In step S12, a process for determining the system state of the emission suppression system 11 is performed, and then it is determined whether the determination process has been completed (step S13). If the answer is negative (NO), the process is terminated, while if the answer is affirmative (YES), the emission suppression system 11 is set to the normal purge mode (step S14) and the process is terminated.

Next, each of the above processing steps will be sequentially described.

(1) Monitoring permission judgment (FIG. 3, step S
1) The monitor permission determination is based on the detected engine coolant temperature TW, intake air temperature TA, engine speed NE, and absolute pressure PB in the intake pipe.
A, it is determined whether the throttle valve opening θTH and the vehicle speed VSP are within predetermined ranges, whether the vehicle is in a cruise running state, and whether purge has been performed for a predetermined time. As a result, it is determined that the monitor permission condition is satisfied when the respective operating parameters are within the predetermined ranges, the vehicle is in a cruise running state, and the purge is performed for a predetermined time, the flag FMON is set to “1”, and otherwise, the flag FMON is set. Is set to “0”.

(2) Checking Tank Internal Pressure When Opening to Atmosphere (FIG. 3, Step S3) FIG. 4 is a flowchart showing a routine for checking the tank internal pressure when opening to the atmosphere. This program is executed during background processing.

First, in step S21, it is determined whether or not the flag FST1 indicating that the initialization has been completed and the check has been started is "1". Since FST1 = 0 at the start of this processing, the flow advances to step S22. Then, the process immediately proceeds to step S23.

In step S22, the discharge suppression system 11 is set to the tank internal pressure release mode, and the second timer tm
The timer value of ATMP is set to "0", the second timer tmATMP is started, and the flag FST1 is set to "1". That is, the two-way valve 28 is opened, the drain shut valve 38 is opened, and the purge control valve 36 is opened to release the tank internal pressure to the atmosphere (see FIG. 2).

Then, in a step S23, it is determined whether or not the timer value of the second timer tmATMP has passed a predetermined time T2. Here, the predetermined time T2 is set to a time during which the internal pressure of the discharge suppression system 11 can be stabilized, for example, 4 seconds. When the answer is negative (NO), the program ends, while when the answer is affirmative (YES), the process proceeds to step S43, where the PT sensor 29 measures the tank internal pressure PATM when the atmosphere is opened. And ECU5
(Step S24), the flag FST1 is set to "0" (step S25), and this check is ended.

(3) Checking tank internal pressure fluctuation (FIG. 3, step S5) FIG. 5 is a flowchart showing a tank internal pressure fluctuation checking routine. This program is executed at the time of background processing.

First, in step S31, it is determined whether or not the flag FST2 indicating that the initialization has been completed and the check has been started is "1". Since FST2 = 0 at the start of this processing, the flow advances to step S32. Then, the process immediately proceeds to step S33.

In step S32, the discharge suppression system 11 is set to the tank internal pressure fluctuation check mode, the third timer tmTP is set to "0", and the third timer tmT
P is started, and the flag FST2 is set to "1". That is, the two-way valve 28 is switched to the closed state (the electromagnetic drive unit 35 is turned off) while the purge control valve 36 and the drain shut valve 38 are kept in the open state, and the discharge suppression system 11 is switched off.
Is set to the tank pressure fluctuation check mode (Fig. 2,
reference).

Then, in a step S33, it is determined whether or not the third timer tmTP has passed a predetermined time T3 (for example, 10 seconds). When the answer is negative (NO), the program is terminated as it is, while when the answer is affirmative (YES), the tank pressure PCLS at the lapse of the predetermined time T3 is measured and stored in the ECU 5 (step S3
4), the first tank internal pressure change rate PV based on equation (1)
ARIA is calculated (step S35).

[0065]

(Equation 1) Then, the first tank internal pressure change rate PVARIA calculated as described above is stored in the ECU 5 and the flag FST2 = 0
(Step S36), the main check is ended.

(4) Tank Internal Pressure Reduction Processing (FIG. 3, Step S7) FIG. 6 is a flowchart showing a tank internal pressure reduction processing routine. This program is executed at the time of background processing.

First, in step S41, it is determined whether or not a flag FST3 indicating that the initialization has been completed and the processing has been started is "1". Since FST3 = 0 at the start of this processing, the processing proceeds to step S42, and thereafter, Immediately follows step S43
Proceed to.

In step S42, the discharge suppression system 11 is set to the tank pressure reduction mode, and the flag FST3 is set to "1". That is, the purge control valve 36 is maintained in the open state, the two-way valve 28 is switched to the open state, and the drain shut valve 38 is switched to the closed state (see FIG. 2). Is set to a mode in which the pressure reduction processing of the emission suppression system 11 is performed. Next, it is determined whether or not the tank pressure PT at this time is equal to or lower than the target pressure P1 (step S43). The target pressure P1 is set to, for example, a value obtained by subtracting a predetermined pressure of 15 mmHg from the detected atmospheric pressure PATM. By setting the target pressure P1 in this manner, the influence of the detection error of the tank internal pressure sensor can be eliminated. If the answer to step S43 is negative (NO), the program ends, while if the answer is positive (YES), the flag FST3 is set to "0" (step S43).
44), the pressure reduction processing ends.

(5) Leakdown Check (Step S10 in FIG. 3) FIG. 7 is a flowchart showing a leakdown check routine. This program is executed at the time of background processing.

First, in step S51, it is determined whether or not a flag FST4 indicating that initialization has been completed and a check has been started is "1". At the start of this processing, since FST4 = 0, the flow advances to step S52. Immediately proceeds to step S53.

In step S52, the emission suppression system 11 is set to the leak-down check mode, the fourth timer tmPST is set to "0" and started, and the flag FST4 is set to "1". That is, the purge control valve 36 is closed while the two-way valve 28 is kept open and the drain shut valve 38 is kept closed to shut off the exhaust suppression system 11 and the intake pipe 2 of the engine 1 ( FIG.
reference).

Then, the process proceeds to a step S53, wherein it is determined whether or not the tank internal pressure (hereinafter referred to as "start pressure") PST at the start of the leak down check is measured. In the first loop, since the answer to step S53 is negative (NO), the process proceeds to step S54, and it is determined whether or not the measured value of the fourth timer tmPST has passed a predetermined time (predetermined delay time) T4 (step S54). S54). If the elapsed time has not elapsed, the program is immediately terminated. After the elapsed time, the process proceeds to step S55, where the start pressure PST is measured and the fifth pressure is measured.
The timer tmLEAK is set to "0" and started.

The reason why the measurement of the start pressure PST is delayed by the predetermined time T4 as described above is that, as shown in FIG. 2D, at the time T4 when the tank internal pressure PT reaches the predetermined pressure P1, the canister internal pressure PC ( = PCMIN) is the predetermined pressure P1
The reason is that the tank pressure PT keeps decreasing even after the time t4 and the tank pressure PT and the canister pressure PC start increasing at the time t5 when the canister pressure PC becomes substantially equal. That is, when the start pressure PST is measured at time t4, a second tank internal pressure change rate PVAR described later is obtained.
This is because accurate measurement of IB cannot be performed, and such a problem can be avoided by measuring the start pressure PST at time t5.

Here, the predetermined time T4 is the same as the purge control valve 3
6 is set to the time required from when the valve 6 is opened to when the tank internal pressure PT and the canister internal pressure PC become substantially equal (the pressures of the respective parts of the discharge suppression system 11 become substantially equal).

Next, it is determined whether or not the fifth timer tmLEAK has passed a predetermined time (predetermined measurement time) T5 (for example, 10 seconds) (step S56). Then, in the first loop, the answer is negative (NO), and thus this program is terminated.

On the other hand, in the next loop, since the answer to the above-mentioned step S53 is affirmative (YES), the process proceeds to step S56, and the fifth timer tmLEAK is set to the predetermined time T.
It is determined whether or not 5 has elapsed. If the answer is negative (NO), the program is terminated as it is, while if the answer is affirmative (YES), the current tank pressure (end pressure) PEND for which a leak down check is being performed.
Is measured and stored in the ECU 5 (step S57), and the second tank internal pressure change rate PVARIB is calculated based on equation (2).
Is calculated (step S58).

[0077]

(Equation 2) Then, the second tank internal pressure change rate PVARIB calculated as described above is stored in the ECU 5, the flag FST4 is set to "0" (step S59), and the check is completed.

(6) System State Determination Processing (FIG. 3, Step S12) FIG. 8 is a flowchart showing an abnormality determination processing routine, and this program is executed during background processing.

First, in a step S61, it is determined whether or not the first timer tmPGR has passed a predetermined time T1 during the pressure reduction processing. If the answer is affirmative (YES), it is determined that a large amount of fuel vapor leaks from the emission suppression system 11 due to "perforation" of the fuel tank 23, etc., and the process proceeds to step S62, where the first Tank internal pressure change rate PVARI
It is determined whether or not A is larger than a predetermined value P2. And
If the answer is negative (NO), it means that the rise in the tank internal pressure at the time of the tank internal pressure fluctuation check is low, and it is determined that a large amount of fuel vapor is leaking from the fuel tank 23 or the pipe connection part, and the emission is suppressed. An abnormality of the system 11 is detected (step S63), and a processing end flag is set (step S6).
6) End this program. On the other hand, if the answer to step S62 is negative (NO), a large amount of fuel vapor is generated at the time of checking the tank internal pressure fluctuation and the tank internal pressure rises (fluctuation).
In this case, the emission suppression system 11 cannot be brought into the predetermined negative pressure state, and the determination is suspended (step S64), the processing end flag is set (step S66), and the program ends.

On the other hand, if the answer to step S61 is negative (NO)
In this case, that is, when the emission suppression system 11 can be set to the predetermined negative pressure state, a predetermined determination processing routine after the completion of the pressure reduction processing is executed (step S65), and a processing end flag is set (step S66). ) Terminate this program.

The determination process routine executed in step S65 is specifically executed according to the flowchart shown in FIG.

First, the second tank internal pressure change rate PVARI
It is determined whether the deviation between B and the first tank internal pressure change rate PVARIA is greater than a predetermined value P3.

That is, the tank internal pressure change rate PVARIB
Is caused by a leak from the emission suppression system 11,
Alternatively, the second tank internal pressure change rate PVARI is used to determine whether the pressure is due to the amount of steam generated in the fuel tank 23.
It is determined whether the deviation between B and the first tank internal pressure change rate PVARIA is greater than a predetermined value P3. That is, if the second tank internal pressure change rate PVARIB is large because the amount of steam generated in the fuel tank 23 is large, the answer to step S71 is negative (NO), and the amount of leakage from the emission suppression system 11 to the outside is large. The second tank internal pressure change rate PVARI
If B is large, the answer to step S71 is affirmative (YES).
Becomes Here, the predetermined value P3 is set as shown in FIG. 10 according to the pressure reduction processing time TR. That is, the predetermined value P3
Is set to "P31" when the pressure reduction processing time TR is longer than the predetermined time TR1, and is set to "P32"(> P31) when the pressure reduction processing time TR1 is shorter than the predetermined time TR. Then, the answer to step S71 is affirmative (YE
S), that is, the second tank internal pressure change rate PVARIB
When the deviation between the pressure and the first tank internal pressure change rate PVARIA is greater than a predetermined value P3, it is determined that an abnormality of the emission suppression system 11, that is, leakage has occurred (step S72), and the answer to step S71 is negative (step S71). If NO), it is determined that the emission suppression system 11 is normal (step S73), and the process ends.

(7) Normal Purge (FIG. 3, Step S14) FIG. 11 is a flowchart showing the setting conditions of each valve in the normal purge mode.

That is, the two-way valve 28, the drain shut valve 39, and the purge control valve 36 are opened to set the normal purge mode, and the air is allowed to be sucked from the engine 1 (step S81). I do.

As described above, according to the present invention, the tank internal pressure after a lapse of a predetermined time T4 (FIG. 2, t5) from the time when the tank internal pressure PT reaches the predetermined pressure P1 (FIG. 2, t4) is defined as the starting pressure PST. Further, the tank internal pressure after a lapse of a predetermined time T5 is set as the end pressure PEND, and the second tank internal pressure change rate PV
Since ARIB is calculated (Equation (2)), an accurate change rate PVARIB can be obtained by eliminating the effect of a decrease in the tank internal pressure PT after the completion of the pressure reduction processing. As a result, the presence or absence of leakage of the emission suppression system 11 can be determined more accurately.

FIG. 12 is a flowchart of the leak-down check process according to the second embodiment of the present invention.
Steps S52 and S54 in the flowchart of FIG. 7 are changed to steps S52a, S54a, and S54b, respectively.

In this embodiment, since the fourth timer tmPST is not used, the initialization of the timer is not performed in step S52a. Further, in step S54a, the amount of change ΔPT in the tank internal pressure is determined by the current detected value PT of the tank internal pressure.
(N) and the difference between the previous detection value PT (n-1).
In a succeeding step S54b, it is determined whether or not the ΔPT value is negative. At the beginning of the main check, since ΔPT <0, the program is immediately terminated. When ΔPT ≧ 0, the routine proceeds to step S55, where the start pressure PST is measured.

According to this embodiment, when the tank internal pressure PT becomes substantially minimum, that is, at the time t5 in FIG.
Since the N value is used as the start pressure PST, an accurate tank internal pressure change rate PVARIB can be obtained as in the embodiment of FIG.

Next, a third embodiment of the present invention will be described with reference to FIGS.

In this embodiment, as shown in FIG. 13, a canister 26 is provided with a canister internal pressure sensor 52 for detecting a canister internal pressure PC, and the detection signal is supplied to the ECU 5.

The tank pressure reduction process is performed by the program shown in FIG. Steps S41 to S4 in FIG.
The process of No. 4 is the same as the process of steps S41 to S44 in FIG.

In FIG. 14, when the answer to step S43 is negative (NO), that is, when PT> P1 is satisfied and the tank internal pressure has not reached the predetermined pressure P1, it is determined whether or not the canister internal pressure PC is equal to or lower than a predetermined lower limit value PCLMT. Determine (Step S
45). As a result, if PC> PCLMT is satisfied and the canister internal pressure PC has not reached the predetermined lower limit PCLMT, the closed state of the drain shut valve 38 is maintained (step S46) (see FIG. 15, t3 to t7). Then P
When the C value has reached the predetermined value PCLMT, the drain shut valve 38 is opened (step S47) (see t7 in FIG. 15), and it is determined whether or not the state has continued for a sixth predetermined time T6 or more. (Step S48). If the open state of the drain shut valve 38 continues for the sixth predetermined time T6 or more, it means that the canister internal pressure PC does not increase even though the drain shut valve 38 is instructed to open. It is determined that an error has occurred, and step S44
Proceed to.

According to the program shown in FIG. 14, when the canister internal pressure PC reaches the predetermined lower limit value PCLMT during the pressure reduction process, the drain shut valve is controlled to open and close, and the PC value becomes approximately PC.
The LMT value is maintained (see FIG. 15, t7 to t4). Thereafter, when the tank internal pressure PC reaches the predetermined pressure P1 (FIG. 15,
t4), the pressure reduction processing ends.

The other points are the same as in the first or second embodiment. However, the fourth predetermined time T4 in the leak-down check process needs to be smaller than that in the first embodiment. Since the canister internal pressure PC does not become lower than the lower limit value PCLMT, the time required until the canister internal pressure PC becomes equal to the tank internal pressure PT is shorter than in the first embodiment.

In this embodiment, since the canister internal pressure PC is detected, the tank internal pressure PT and the canister internal pressure P are detected.
When the difference from C becomes substantially zero, the start pressure PST of the leak down check may be measured.

According to the present embodiment, since the canister internal pressure PC and the tank internal pressure PT do not excessively decrease, that is, the inside of the discharge suppression system 11 does not become excessively negative, the reliability of the discharge suppression system 11 is reduced. Can be improved.

In the above-described embodiment, the presence or absence of leakage of the discharge suppression system 11 is determined based on the tank internal pressure PT. However, when the canister internal pressure sensor 52 is provided (third embodiment), A value corresponding to the second tank internal pressure change rate PVARIB may be calculated based on the canister internal pressure PC. As shown in FIG.
This is because after 5 the canister internal pressure PC and the tank internal pressure PT become substantially equal.

Further, the presence or absence of leakage of the discharge suppression system 11 may be determined using only the canister internal pressure sensor 52 without using the tank internal pressure sensor 29. In this case, the decompression process is performed until the detected pressure of the canister internal pressure sensor 52 is reduced by a predetermined pressure from the detection pressure when the discharge suppression system 11 is in the open-to-atmosphere state. Canister internal pressure P after elapse of time T4
When the rate of increase of C is equal to or greater than a predetermined value, it is determined that leakage has occurred.

[0100]

As described in detail above, according to the first aspect of the present invention, the evaporative fuel treatment system according to the first aspect has a negative pressure after a lapse of a predetermined delay time from the time when the decompression process for setting the evaporative fuel discharge suppression system to the predetermined negative pressure state is completed. Since the presence or absence of leakage of the evaporative fuel emission suppression system is detected based on the pressure reduction rate, the effect of the fact that the internal pressure of the fuel tank decreases even after the completion of the pressure reduction process is eliminated, and more accurate detection of the presence or absence of leakage is performed. Detection can be performed.

According to the second aspect of the present invention, the evaporative fuel discharge suppression system is configured such that the pressure detected by the pressure detecting means is a predetermined pressure relative to the detected pressure when the evaporative fuel discharge suppression system is open to the atmosphere. Therefore, even if there is a detection error in the pressure detecting means, its influence can be eliminated. As a result, a constant pressure reduction with respect to the atmospheric pressure can be accurately performed.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram showing one embodiment of an evaporative fuel processing apparatus for an internal combustion engine according to the present invention.

FIG. 2 is a diagram showing an operation pattern of a control valve and changes in a tank internal pressure and a canister internal pressure.

FIG. 3 is a flowchart showing a main routine of the present invention.

FIG. 4 is a flowchart of a tank internal pressure check routine at the time of opening to the atmosphere.

FIG. 5 is a flowchart of a tank internal pressure fluctuation check routine.

FIG. 6 is a flowchart of a tank pressure reduction processing routine.

FIG. 7 is a flowchart of a leak down check routine.

FIG. 8 is a flowchart of a system state determination processing routine.

FIG. 9 is a flowchart of an abnormality determination processing routine.

FIG. 10 is an abnormality determination map.

FIG. 11 is a flowchart of a normal purge routine.
You.

FIG. 12 is a flowchart of a leak down check routine according to a second embodiment of the present invention.

FIG. 13 is a diagram showing a configuration around a canister according to a third embodiment of the present invention.

FIG. 14 is a flowchart of a tank internal pressure reducing process routine according to a third embodiment of the present invention.

FIG. 15 is a diagram showing an operation pattern of a control valve and changes in a tank internal pressure and a canister internal pressure in a third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Internal combustion engine 5 Electronic control unit (ECU) 10 Purge passage 11 Evaporation fuel discharge suppression system 23 Fuel tank 25 Inlet 26 Canister 27 Fuel vapor flow passage 28 Two-way valve 29 Tank internal pressure sensor 36 Purge control valve 38 Drain shut 52 Canister internal pressure Sensor

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Kazunori Sawamura 1-4-1 Chuo, Wako-shi, Saitama Prefecture Inside Honda R & D Co., Ltd. (72) Inventor Yoshitaka Kuroda 1-4-1 Chuo, Wako-shi, Saitama Inside Honda R & D Co., Ltd. (56) References JP-A-4-153554 (JP, A)

Claims (5)

(57) [Claims] 1. A canister having a fuel tank, an intake port communicating with the atmosphere, and having activated carbon for adsorbing evaporated fuel generated in the fuel tank, and a first passage connecting the canister and the fuel tank. A second passage connecting the canister to an intake system of the internal combustion engine;
An evaporative fuel discharge suppression system comprising a purge control valve interposed in a passage of the drain passage valve for opening and closing the intake port of the canister; and a pressure detecting means for detecting a pressure in the evaporative fuel discharge suppression system. Opening the purge control valve and closing the drain shut valve to introduce a negative pressure in the intake pipe of the engine to set the evaporative fuel discharge suppression system to a predetermined negative pressure state, and thereafter the purge control valve An internal combustion engine comprising: a pressure reduction processing means for closing a valve; and a leakage detection means for detecting the presence or absence of leakage in the evaporative fuel emission suppression system based on a decrease rate of the negative pressure after closing the purge control valve. The evaporative fuel processing apparatus according to claim 1, further comprising a delay means for operating the leak detection means when a predetermined delay time has elapsed from the end of the pressure reduction processing by the pressure reduction processing means. Emissions of the fuel vapor processing apparatus. 2. The pressure reduction processing means operates until the pressure detected by the pressure detection means drops by a predetermined pressure with respect to the pressure detected when the evaporative emission control system is open to the atmosphere. The fuel vapor treatment device for an internal combustion engine according to claim 1, wherein 3. The leak detecting means detects a pressure in the evaporative fuel discharge suppression system at the start of operation and a pressure in the evaporative fuel discharge suppression system when a predetermined measurement time has elapsed from the start of operation. 2. The apparatus according to claim 1, wherein the presence or absence of the leakage of the fuel vapor emission suppression system is detected based on the information. 4. The apparatus according to claim 1, wherein the predetermined delay time is a time until the pressures of respective parts in the fuel vapor suppression system become substantially equal. 5. The apparatus according to claim 1, wherein the pressure detecting means is at least one of a tank internal pressure detecting means for detecting a pressure in the fuel tank and a canister internal pressure detecting means for detecting a pressure in the canister. 5. The fuel vapor treatment device for an internal combustion engine according to any one of claims 4 to 4.